The present invention relates to a release bearing unit suitable for a clutch of an automobile.
FIG. 8 shows a conventional release bearing unit by way of example. A release bearing 1 and a release hub 2 are provided. The release hub 2 may generally be a casting made of cast iron or aluminum. The release hub 2 is provided with a cylinder 3 to whose circumference the release bearing 1 is fitted, a fork guide 5 to whose circumference a release fork of the clutch (shown in a dashed line in FIG. 8) is coupled, and a projection 6 receiving operation force from the release fork 4 and supporting a side of the release bearing 1.
As shown in FIG. 9, the fork guide 5 is provided with a pair of parallel flat portions 5a and 5b and portions 5c and 5d. Since the release hub 2 is operated to slide on a retainer made of aluminum alloy, an inner face 7 of the release hub 2 should be finished precisely.
The above-constructed conventional release bearing unit has the following problems. Depending on the type of automobile to be used, the length A of the release hub 2 as shown in FIG. 8 must be altered. Therefore, a plurality of types of release hubs 2 having a different clearance A must be prepared for each of the plurality of types of automobiles. Further, because the structure of the release hub 2 is complex, it is difficult to make it light although a light release hub 2 has been recently desired. In order to reduce abrasion of the retainer made of aluminum alloy and prevent the stepping force of the clutch pedal from becoming abnormal, the inner face 7 of the release hub 2 is fairly precisely finished. However, it is not enough, and the inner face 7 should be greased. It is difficult to have a release bearing unit with these properties.